The present invention relates to a phase-shifting motor for rotary equipment and, more particularly, to an actively-controlled, permanent-magnet actuator for controlling an aspect of an item of rotating machinery by varying the phase of the motor rotor with respect to the rotation of the rotating machinery.
Fundamental to the operation of many rotating machines, devices, or instrumentalities is the ability to control some aspect of the rotating portion of the instrumentality, device or machine. For example, many turbine or fan devices have facility for dynamically controlling the angle-of-attack of their rotor blades. Angle-of-attack is a factor in determining the dynamic forces acting on the blade and, hence, determining the forces applied by the blades to the frame of the instrumentality.
Control of blade angle-of-attack generally originates in the non-rotating frame of the instrumentality, rather than in the rotating coordinate reference frame of the rotating part of the instrumentality. For example, control of the variable pitch or the angle-of-attach of the blades of, for example, a wind turbine, a ship or airplane propeller, the main rotor or the torque-reaction fan or tail rotor of a helicopter are all originated within the frame of the instrumentality (e.g. the mast of a wind turbine, the airframe of an airplane or helicopter, or the engine room of a ship).
A method of bridging from the non-rotating frame to the rotating frame is required and many such bridging systems have been known for a long time. It is often a tricky mechanical engineering problem to introduce control signals or movements into a mechanism that is mounted on and turning with a rotating drive shaft. A common example of such a problem is controlling the pitch of the blades of a ship""s screw propeller, an airplane propeller, a wind-driven turbine, or a helicopter""s main lift rotor or torque reaction (tail) rotor. A related example is the control of leading or trailing edge flaps on either fixed pitch blades or on blades with controllable pitch.
U.S. Pat. No. 5,281,094, granted on Jan. 25, 1994, to McCarty, et al. discloses an arrangement for varying the pitch of fan blades. The blades are rotated by a main drive shaft which rotates a differential gearbox, and by rotating the gearbox, rotates the blades. A concentric shaft also enters the differential gearbox. The concentric shaft is normally locked so as to rotate with the main drive shaft. However, when the concentric shaft is unlocked, it is either rotated faster than the main drive shaft by an electric motor or braked by an electric brake so as to rotate slower than the main drive shaft. Relative rotation of the two shafts operates through the differential aspect of the gearbox in order to increase or decrease the pitch of the fan blades. When the desired blade pitch is attained, the two shafts are again locked together so as to rotate as one. U.S. Pat. No. 5,595,474, granted on Jan. 21, 1997, to Girard discloses a comparable mechanism.
As far back as the 1940s, in the helicopter art, U.S. Pat. No. 2,443,393, granted on Jun. 15, 1948, to Landgraf, disclosed a complex mechanical system for duplicating the effect of the cyclic pitch control of a helicopter by controlling trailing-edge flaps (ailerons) on the main rotor blades to affect maneuvering control of the craft.
U.S. Pat. No. 5,409,183, granted on Apr. 25, 1995, to Gunsallus, discloses using a computer with blade-response feedback and electric-to-hydraulic converters in order to control a leading-edge flap on a helicopter blade so as to affect instantaneous or cyclic blade pitch control.
U.S. Pat. No. 5,584,655, granted on Dec. 17, 1996, to Deering discloses affecting the instantaneous pitch or axis angle of a wind turbine blade by various means, in order to reduce excessive loadings due to gusty conditions.
U.S. Pat. No. 5,588,800, granted on Dec. 31, 1996, to Charles, et al. discloses the use of a trailing-edge flap near the tip of a helicopter main rotor blade to control blade vortex interaction noise.
In each of the above cases, complex arrangements are necessary to achieve the desired degree of control out at the end of a rotating shaft.
It is an object of the present invention to generate a mechanical control signal with respect to a rotating shaft from a signal source that is stationary with respect to the rotation of the shaft.
It is another object of the present invention to generate a mechanical control signal, with respect to a rotating shaft, using a transducer that occupies a minimum of axial space along the length of the rotating shaft.
It is yet another object of the present invention to generate a mechanical control signal, with respect to a rotating shaft, that is substantially equally effective at various rotational shaft speeds over the normal range of said rotational shaft speeds.
It is still yet another object of the present invention to generate a mechanical control signal, with respect to a rotating shaft, that is minimally subject to dynamic loads due to the speed of rotation of the shaft.
It is yet still another object of the present invention to generate a mechanical control signal, with respect to a rotating shaft, that is minimally subject to wear.
Still another object of the present invention is to generate a mechanical control signal, with respect to a rotating shaft, that requires a minimum of maintenance and adjustment.
Yet another object of the present invention is to generate a mechanical control signal, with respect to a rotating shaft, that operates at a rate that is at least of the same order of magnitude as the rotational speed of the shaft.
These and other objects and purposes are achieved by an electromagnetic actuator with rotor and stator portions, said rotor rotating substantially at the same average speed as the rotating shaft, with a plurality of alternately-reverse-pole permanent magnets at its perimeter and by a method of operating said actuator. A plurality of electromagnets on the stator are energized to develop a magnetic polarity of polarized areas adjacent to the poles of the permanent magnets and that reverses polarity at a frequency proportional to the rotational speed of the rotor each time that a permanent magnet on the rotor advances from one electromagnet to the adjacent electromagnet. The phasing of either the reversals or the magnitude of the energization of the electromagnetic devices being variable with respect to the rotation of the shaft so as to control the phasing of the instantaneous rotational position of the rotor with respect to the shaft, with linkage connecting the rotor to an instrumentality, for moving the instrumentality with respect to the shaft in response to a change in the phasing of the instantaneous rotational position of the rotor with respect to the shaft.